This invention relates to novel glass compositions formed from oxides of aluminum, boron and phosphorous.
A large number of oxide systems, particularly those including silicon have been utilized to form glass compositions. As is well known, glasses exhibit a wide variety of physical characteristics including optical properties, electrical properties, chemical properties, solubility for modifiers and heat stability which enables the practitioner to choose a particular glass to fit his needs. Usually, glass compositions have limited desirable physical characteristics so that the practioner must provide some means for ameliorating the poor physical properties of the composition in order to take advantage of the desired properties which the glass composition provides. For example, most silicate glasses which have relatively high annealing temperatures also generally have low thermal expansion coefficients.
Aluminum borophosphate glass compositions are known in the art. For example, U.S. Pat. No. 3,519,445 discloses an aluminum borophosphate glass-ceramic composition which is disclosed to contain 50 to 80 weight percent P.sub.2 O.sub.5. The composition is formed in open silica crucibles at 1500.degree.-1650.degree. C. and therefore contains silica in the composition which is derived from the crucible. Volf in Technical Glasses, pages 401-402, SNTL Publishers, Prague and Sir Isaac Pitman, London (1961) discloses aluminum borophosphate glasses containing 10 to 30 mole percent of mixtures of alkali or alkaline earth modifiers which are required for homogeneous glasses. Dale et al., J. Soc. Glass Technology, Vol. 35, pages 185-192 (1952) disclose aluminum borophosphate glasses containing low concentrations of P.sub.2 O.sub.5 and containing up to about 30 mole percent of mixture of alkaline earth modifiers, e.g. MgO and CaO which are required to form homogeneous glasses.
It would be desirable to provide glass compositions which provide a wide variety of desirable physical properties. Furthermore, it would be desirable to provide such glass compositions to which can be added modifiers to improve a desired physical characteristic of the glass without degrading other physical characteristics of the glass.